A typical train includes one or more locomotives pulling a plurality of load cars. Each vehicle in the train includes a plurality of steel wheels that roll along the metal rail as the train is propelled along the track. Proper interaction between the wheel and the rail is critical for safe, reliable, efficient operation of the train.
A rail includes a bottom mounting flange, a top railhead that makes contact with the vehicle wheel, and a flange interconnecting the flange and the railhead. A vehicle wheel includes a center hub mounted onto the vehicle axle, a plate extending outwardly from the hub, and an outer rim surrounding the plate for making contact with the rail. The rim includes an outside diameter tread that may be flat or tapered and a flange extending outwardly from a back side of the tread. The tread rides along a top surface of the railhead for supporting the vertical weight of the vehicle. The flange extends along and makes contact with a side of the railhead for providing lateral support to allow the wheel to follow along the path of the railhead. Flanges are provided on only one side of each wheel along an inside of the rail.
Rail, or railroad, vehicle wheels suffer wear over time due to their contact with the rail. The treads wear as a result of their contact with the top of the rail, particularly in the event of the wheel slipping with respect to the rail during acceleration or braking events. The wheel flanges will wear due to their contact with the inside surface of the railhead, particularly on curves and through switches. Consequently, rail wheel wear must be monitored to ensure that dimensions of the wheel subject to wear are sufficient for continued safe use.
In the past, rail wheel dimensions were periodically measured using a Federal Railway Administration (FRA) approved mechanical gauge. More recently, mechanical gauges have been replaced with electronic gauges that provide more accurate and repeatable rail wheel measurements for determining proper positioning on the wheel and to measure rail wheel dimensions such as rim thickness, flange thickness, flange height, and distance from reference groove (also called witness groove) of a locomotive wheel. With both mechanical gauges and electronic gauges, a key measurement that is needed to determine the other rail wheel dimensions is the reference groove diameter since the reference groove diameter is typically used as a reference when determining wheel diameter by adding 2 times the distance from reference groove.